Hygroscopic control device



Feb. 27, 1951 R. T. SQUIER 2,543,384

HYGROSCOPIC common DEVICE Filed March 29, 1948 2 Sheets-Sheet 1 (Ittorneg Feb. 27, 1951 R. T. SQUIER' 2,543,384

HYGROSCOPIC CONTROL DEVICE Filed March 29, 1948' 2 Sheets-Sheet 2 Fig.9,

Gttorneg Patented Feb. 27, 1951 UNITED STATES PATENT OFFICE Minneapolis-Honeywell Regulator Company,

Minneapolis, -M inn., a corporationof Delaware Application March 29, 1948, Serial N0. 17 ,622

8 Ciaims. l

The present invention relates to hygroscopic control devices and more'parti'cu'larlyto improvements in humidity responsive elements or units of the resistance type.

.Humidity'regulators and indicators of the resistance salt type are old, but the. inaccuracies in them due to variations in resistance of the conductive coatings, the expense of calibration,

the instability of calibration, and the difiiculties in reproduction within given ranges of operation have greatlylimited their usage.

'It is therefore an object-of this invention to provide an improved hygroscopic control unit or element of the resistance type.

It is an object of the present invention to provide a hygroscopic unit in which theconductor elements are so positioned as to'perinita uniform conductive and hygroscopic coating therebetween.

It is also an object of this invention to proyide 'a hygroscopic unit Witha conductive element or coating of uniform thickness and resistance.

It is still further .an object of this inverition to provide a hygroscopic'unit in which the conductors are embedded or impressed into =a moisture impervious base material'to facilitate anniform conductive or hygroscopic coating thereupon.

-'Another object of this invention is to :provide in a humidity sensitive unit substantially flat conductors flush with the surface oithe moisture impervious mounting element to facilitate uniformity of coating'of the hygroscopic material.

Still another object of this invention-is toprovide a humidity sensitive unit of the resistance type having a hygroscopic and conductive film and a moisture permeable film enclosing the same "to protect the hygroscopic film.

A further object of this invention is to provide ahygroscopic controldevice of the resistance type which gives a rapid response to "changes in humidity or moisture.

It is also an object of this invention to provide a hygroscopic control device .of the resistance type vlhichiis :sensitive to .-:small changes in the conditi'on of humidity.

A still further object of this invention is to provide a hygroscopic control device of the resistance type with improved accuracy, sensitivity and rapidity :o'f response which is easily reproduced .by mass production at greatly reduced cost.

It is also an object of this invention to :provide a humidityresponsive unit of .thelres'istance type in which *the conductors are .formed by stamping or pressing foil of a conductive material into a suitable moisture :impervious base unit or by fillinggrooves in saidbase'with a suitable conductive material.

A further object of this invention is'to provide, in a hygroscopic :control device, amounting means such .that the elements may be readily installed 'or replaced, so that a plurality of elements maybe mountedinadjacent position, and whereon one or more of the elements may be so mounted that the maximum surface of said elements is exposed to the circulating surrounding air.

It is also an object of *thisinvention to ,pro vide an improved method of making sucha humidity responsive elem'ent ofthe salt :resistanc'e type.

These and other objects, advantages and :features of this invention will becomeapparent upon study of the following specification and drawings wherein:

Figure l is an elevation view of the-humidity control device and-its associatedmounting structure, with partsbroken away.

Figure 2 is an end elevation "view of the device of Figure 1, with parts broken away.

Figure 3 is anenlarged view of the humidity responsiveelement detached from its mounting structure.

Figure 4 is a sectional view taken .along the line 4--4 of Figure 3 and showing :the connection between a conductor anda conductive .eyeletor mounting sleeve.

Figure 5 is an enlarged cross-sectional View of the portionof the humidity responsive element showing the conductors, the hygroscopic conductive coating and the protective coating covering the same.

Figure 6 is a modification of the preferred embodiment of this invention, still further enlarged, disclosing the use of two layers of conductor material to form the conductors of the humidity responsive element.

Figure '7 is a sectional view of still another embodiment of the humidity responsive'element in which grooves are machined into the .moisture impervious material of the element'andthe conductors are formed of a paste comprising colloidal graphite.

Figure 8 shows generally a press.

Figure 9 shows the method of dipping.

The present humidity control device it comprises, generally, a mounting or base portion H, a :humidity responsive resistance element l2,

and a cover I3, element I2 being an improvement over the hygroscopic elements disclosed in the Dunmore Patents No. 2,285,421, dated January 9, 1942, and No. 2,295,570, dated September 15, 1942.

The base portion I I includes an insulating strip I6 having spaced prongs I'iI8 attached thereto which extend outwardly from the plane of the base portion and perpendicular to it. Prongs I'i-IB have flexible sides so that eyelets or mounting sleeves 2I in the element I2 may be pushed over said prongs, with said flexible sides frictionally engaging said eyelets for securing the element I2 to base II and for making electrical connections between the element and said prongs; Lead wires 22-23 connect the prongs II--I8, respectively, to terminals 24-45 mounted on base portion II. Cover I3 is similar to a thermostat cover in that it has slots 26 in the top and bottom to give free access of the circulating air to the element. It fits over the element I2 and is secured to base II in a suitable manner, not shown, to enclose and protect the device. A mounting bracket 27 attached to base II permits mounting the device on any suitable surface, such as the wall of a room.

In the preferred embodiment, element I2 in cludes a relatively thin block or strip of electrically insulating and moisture impervious material, such as polystyrene, having a substantially flat and uniform surface. Element I2 may be of any suitable shape but a rectangular member has been found most convenient. The thickness of element I2 is not critical but should be adequate to provide sufficient strength for manufacturing operations and handling. Conductors 3 I32, of electrically conductive thin foil or leaf material, are embedded in the surface of the element in a grid-like pattern including interlaced finger portions 3334. The eyelets 2I which extend through holes 36-31 in element I2 are crimped over to contact the conductors 3I32 and provide electricalconnections between said conductors and prongs I'II8.

The conductors 3I-32 are embedded in element I2 to a suflicient depth to provide a substantially flush surface for facilitating the application of a coating 38 of hygroscopic material over the conductors. The uniformity of this coating is highly important because it is essential for accuracy in calibration and fast response that uniform amounts of resistance material be placed between each of the finger-like portions 3334 of the conductors 3I32, respectively. Any lack of uniformity will vary both the rate of resistance change and the total change in the resistance value of the element I2 in response to humidity changes, thus destroying the accuracy of its controlling effect. The fiat surface of the element I2 and the positioning of the conductors therein permit the application of this necessary uniform coating, in a manner which will be later described.

Preferably a protective film or coating 40 is formed over the hygroscopic coating 38 on element I2 to guard against damage to the underlying conductive coating. This protective film or coating 40 obviously must be moisture permeable but should also be insoluble in the solvent to be used for cleaning, such as ether, alcohol, or the like. Various materials are suitable for this purpose but good results have been obtained with a solution said to comprise a vinyl-acetate in ethyl alcohol, obtained from the Minnesota Mining and Manufacturing Company and designated by Specification RD-816. Such a coating has but little retarding effect on the conductive film or coating 38 and permits the element I2 to be cleaned of grease, lint, dust or other accumulations that might eventually interfere with proper operation of said element. This protective coating may be formed by spraying or dipping, with care being taken to keep the thickness of the coating uniform to permit uniformity of passage of moisture therethrough. It has also been found that the protective coatings tried, including that above described, tend to stabilize the elements and improve their aging characteristics.

In the manufacture of these elements, the following procedure has been found suitable to give the improved characteristics and performance recited above. The blank strip or block or polystyrene is machined or cut to provide substantially fiat, or otherwise uniform surface, and the block is then accurately sized. The working or upper surface of the block or strip is then slightly roughened by sanding for the purpose of better adhesion of the gold leaf later to be applied. Holes are then drilled in the block or blank through which the mounting eyelets will later be placed. The blanks are then annealed to remove the stresses set up in the material durin the machining operations and subsequently cleaned with chromic acid, rinsed with water and allowed to dry.

The next step in the operation is the embedding or embossing of the conductors into the surface of the blank. In the present application it has been found that gold leaf or foil of a commercial grade, approximately .0006 inch in thickness, makes a desirable conductor. Such a foil is obtainable in tape form on a plastic backing or ribbing, the foil having a varnish coating on its other side. The conductors may take any suitable shape or form but it has been found preferable to use a grid-like conductor structure with interspaced finger portions 33-34. This arrangement is best shown in Figure 3 and is used to insure accurate positioning and spacing of the conductors to provide for equal amounts of hygroscopic salt and equal resistance between the conductors. Figure 8 shows generally a press I 00 which could be used for the embedding process. A die IDI out in the form of the grid-like conductors shown and carried in press I00 is used for embedding the conductors 3I32 into the element I2. The die and conductor are exaggerated in Figure 8 for the purpose of clarity. This is done, as shown in Figure 8, by placing the foil tape I 02 over the element, varnish side down and backing up, with the die heated, as by heater I03, above the tape and parallel to the surface of the element, the die then being forced downwardly to press the foil into the polystyrene base material to form the desired pattern of conductors. The base material becomes somewhat softened by the heat and the foil conductors are cut from the tape and impressed into the surface of the element I2 to a depth such that their upper surfaces are substantially flush with the surface of element I2, as can be seen in Figure 5 and Figure 8. With a substantially fiat or flush surface on the element I2, accurate positioning of the conductors 3I--32 is readily obtained. Good results have been obtained in the above operation with approximately 700 pounds per square inch pressure on the die, approximatel 230 F. temperature of the die and a dwell time of approximately two seconds. The backing strip is then pealed off, leaving the foil conductors embedded in the element. After sufiicient cleaning of the surface of conductors :3l-'32 to :make good electrical contact, eyelets .21 are then inserted through the holes 36-3'l and crimpedover their respective conductors, these eyelets "being made of silver plated brass. The blanks are then annealed again to relieve the stresses set up there in due to the embedding and crimping operations. Next, the blanks are cleaned with a :suitable cleaning material, such as clear naphtha or gasoline, rinsed with alcohol, and then rinsedywith water and dried.

The-next phase of procedure comprisesdipping the element or blank into a hygroscopic salt solution such .as described in the previously mentioned Dunmore patents and :shown schematically inFigure 9. The solution usedecomprisesilithium chloride, polyvinyl alcohol and water, theproportions being varied depending on the range through which the element is designed-to operate. In this dipping process, the (block I2 is inserted into the liquid in a container I01 .in such a manner that all of the exposed surface of the interspaced finger portions of the conductors is immersed with the exception of a portion of one eyelet by which the block is suspended in the solution. The block is withdrawn at a uniform and timed rate by any suitable means such as a motor I08 to insure uniformity of coating and to obtain a predetermined thickness of deposit. The excess of the solution remaining on the edges of the block is then blotted off and the unit dried. The beforementioned protective coating may then be applied in the same manner as above, or otherwise formed. After the protective coating has been applied and the unit dried, the eyelets are cleaned, if necessary. The elements are then seasoned or aged for two or three months by storing in a controlled atmosphere before they are ready for use.

Since the elements l2 are readily installed by merely slipping the eyelets of the element on the prongs 11-48, the can be made relatively thin and several such units can be connected in parallel by merely slipping them over the pegs or prongs 51-48.

The modification of Figure 6 uses two layers of leaf or foil material to form the conductors of the element. This modification permits an increase in conductor cross section without using thicker foil and this avoids some manufacturing difficulties, in addition to decreasing the internal resistance of element. The method of making this modified element is substantially that described above but includes a repetition of the embossing or embedding of the conductors prior to application of the hygroscopic and protective coatings.

The modification of Figure '7 discloses a similar sensing element which is formed by a slightly different process. In this modification grooves are machined into the surface of the element in the form of the grid-like conductors of the preferred design, or its equivalent, and the grooves are filled with a colloidal graphite paste to form conductors 42. These graphite conductors are made with their exposed surfaces substantially flush with the surface of the element as in the previously described elements, so that hygroscopic coating 38 and the protective coating 46 may be applied as recited above. With the exception of the conductor material and the method of forming the conductor 42, this element is substantially the same as those described above. Obviously, because the graphite material has higher resistance than the gold leaf ordinarily used, con- 6 ductors 42 have considerably :more cross sec tional area'than the conductors 3l232.

While I have disclosed the preferred form of my invention, and in addition have shown two modifications, it is to be understood that changes may be made in the shape of the element, the conductors, and the materials without departing from the scope of the invention. Hence the scope of the invention should be determined only by the appendedclaims.

I claim as my invention:

1. A hygroscopic unit comprising, in combination, a base memberof water impervious material, a pair of spaced metallic electrical conductors arranged on said member, spaced terminal means connected to each of conductors, a thin film of hygroscopic material of a sort rendered electrically conductive in the presence of vapor extending between said conductors, and a thin protective coating covering said. film, said coating being permeable to water vapor-but relatively-insoluble in water.

2. A hygroscopic unit comprising in combination, a base member of water impervious material, said member having a plurality of uniformly spaced grooves in its surface, electrical conductive material positioned in said grooves so that the surface of said conductive material is substantiallyflush with the surface of said base member thus providing a relatively smooth surface on said base member, and a uniform coating of hygroscopic material in electrical conductive relation with said electrical conductive material in said grooves, said coating being of a sort rendered conductive by the presence of moisture.

3. A hygroscopic unit comprising in combination, a base member of water impervious material having a flat surface, said base member having a plurality of grooves in said surface, electrical conductive material positioned in said grooves and arranged so that the surface of the same is substantially flush with the surface of said base member providing a substantially uniform fiat surface of said base member, a coating of hygroscopic material extending over said fiat surface and positioned in electrical conductive relation with the electrical conductive material in said grooves, and a moisture permeable and water insoluble protective coating covering said hygroscopic conductive coating.

4. A hygroscopic unit comprising in combination, a base element 01" water impervious material, said element having a plurality of grooves in the form of a grid consisting of a pair of main channels and a plurality of appending minor channels connected thereto and so positioned that the minor channels of one are interspaced with the minor channels of the other, said grooves b ing filled with an electrical conductive paste material to the surface of said base element to form a pair of electrical conductors substantially fiush with the surface of said element, and a thin coating of hygroscopic material in electrical conductive relation with said. conductors, said coating being of a sort rendered electrically conductive by the presence of moisture.

5. A hygroscopic unit comprising in combination, a base element of water impervious material, said member having a plurality of grooves in the form of a grid consisting of a pair of'main channels and a plurality of app-ending minor channels connected thereto and so positioned that the minor channels of one are interspaced with the minor channels of the other, said grooves being filled with a plurality of layers of thin metal to form a pair of electrical conductors substantially flush with the surface of said base member, an electricall conductive microscopically thin hygroscopic coating over at least a portion of said conductors, and a moisture permeable and water insoluble protective coating covering said hygroscopic conductive coating and said conductors.

6. A hygroscopic unit as defined by claim 1 Where in the hygroscopic film comprises a mixture of a Water soluble salt and a suitable film forming material.

7. A hygroscopic unit as defined by claim 1 wherein the hygroscopic film comprises a mixture of a Water soluble salt and a suitable film formin material and wherein the protective coating comprises an organic plastic material different from said film forming material.

8. A hygroscopic unit as defined by claim 1 wherein the protective coating comprises an organic plastic material.

RALPH T. SQUIER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 392,794 France Nov. 13, 1888 636,203 Helberger Oct. 31, 1899 713,607 Coleman Nov. 18, 1902 351,440 Rivers Apr. 23, 1907 1,633,647 Row June 28, 1927 1,739,246 Majce Dec. 10, 1929 1,992,056 Colbie Feb. 19, 1935 2,047,638 Kott July 14, 1936 2,056,928 Magdziarz Oct. 6, 1936 2,166,879 Schmalz July 18, 1939 2,295,570 Dunmore Sept. 15, 1942 2,367,561 Bouyoucos Jan. 16, 1945 2,410,361 Prance Oct. 29, 1946 2,423,476 Billings et a1. July 8, 1947 2,427,144 Jansen Sept. 9, 1947 Certificate of Correction v February 27, 1951 Patent No. 2,543,384

RALPH T. SQUIER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 68, for the Word element read member;

and that the said Letters Patent should be read as corrected above, so that conform to the record of the case in the Patent Office.

the same may this 15th day of May, A. D. 1951.

Signed and sealed THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents.

Certificate of Correction Patent No. 2,543,384 February 27, 1951 RALPH T. SQUIER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 68, for the word element read member;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 15th day of May, A. D. 1951.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

